U.S. Pat. No. 3,051,327 describes a gripper of this kind comprising a support, articulated parallelograms which are disposed in planes converging towards an axis and a first arm of which is mobile with respect to the support parallel to this axis, the opposite arm being mobile in a direction perpendicular to said axis, but fixed in the direction of this latter, and having a clamping finger and means carried by the support for moving the first arm of the parallelogram.
When the first arms of the parallelograms are moved with respect to the support, the opposite arms move with their clamping finger towards or away from the axis of convergence of the parallelograms. In the first case, the fingers may grip a work piece to be transported disposed in this axis. In the second case, the fingers may grip a piece comprising a circular bore, by being engaged in this bore.